linux-kernel - Re: [PATCH 1/4] sched/topology: SD_ASYM

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Message-ID: <0d9598fa-28c1-0851-4d40-2cc97a5317b5@arm.com>
Date:   Tue, 24 Jul 2018 09:59:21 +0100
From:   Qais Yousef <qais.yousef@....com>
To:     Morten Rasmussen <morten.rasmussen@....com>
Cc:     vincent.guittot@...aro.org, peterz@...radead.org,
        linux-kernel@...r.kernel.org, dietmar.eggemann@....com,
        mingo@...hat.com, valentin.schneider@....com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/4] sched/topology: SD_ASYM_CPUCAPACITY flag detection

On 24/07/18 09:37, Morten Rasmussen wrote:
> On Mon, Jul 23, 2018 at 05:07:50PM +0100, Qais Yousef wrote:
>> On 23/07/18 16:27, Morten Rasmussen wrote:
>>> It does increase the cost of things like hotplug slightly and
>>> repartitioning of root_domains a slightly but I don't see how we can
>>> avoid it if we want generic code to set this flag. If the costs are not
>>> acceptable I think the only option is to make the detection architecture
>>> specific.
>> I think hotplug is already expensive and this overhead would be small in
>> comparison. But this could be called when frequency changes if I understood
>> correctly - this is the one I wasn't sure how 'hot' it could be. I wouldn't
>> expect frequency changes at a very high rate because it's relatively
>> expensive too..
> A frequency change shouldn't lead to a flag change or a rebuild of the
> sched_domain hierarhcy. The situations where the hierarchy should be
> rebuild to update the flag is during boot as we only know the amount of
> asymmetry once cpufreq has been initialized, when cpus are hotplugged
> in/out, and when root_domains change due to cpuset reconfiguration. So
> it should be a relatively rare event.


Ah OK I misunderstood that part then.

The series LGTM then.

-- 
Qais Yousef